1. Field of the Invention
The present invention relates generally to electrically conductive sheet molding compound compositions and methods of forming the compositions and, more particularly, to an electrically conductive sheet molding compound composition including conductive carbon black adapted for electrostatic painting.
2. Discussion of the Related Art
Electrostatic painting of various automobile parts, including doors and hoods, is commonly used today in the automotive industry. Electrostatic painting of sheet molding compound (SMC) substrates, for example, is desirable because it reduces paint waste and emissions as compared to non-electrostatic painting techniques. Electrostatic painting techniques require the substrate to be electrically conducting or to have an applied prepcoat or primer which is electrically conducting in order to display an increased paint transfer efficiency. Currently, an electrically conductive primer must be applied to a sheet molding compound composition article to be coated prior to electrostatically painting the article because, unlike steel, sheet molding composition is not conductive.
When using an electrically conducting primer, the path to ground is achieved via the conducting primer. An alternative technique is to use a grounding clip. This undesirably causes higher film builds near the grounding clip with film builds decreasing as the distance from the grounding clip increases. In addition, after several passes through the paint booth, significant resistance to ground may be encountered due to multiple paint layers on the buck itself.
There thus exists a need in the art to provide a sheet molding compound composition material with increased electrical conductivity. This would overcome problems associated with electrostatically painting articles whose electrical conductivity is provided only through a conductive primer or prep coat. These problems include excessive waste of paint as a result of the need for overspraying, increase in pollution, and the inability to evenly coat the substrate. Although the general idea of conductive sheet molding compound has been previously suggested, problems exist in obtaining uniform conductivity within a molded part, resulting in poor paint adhesion. The present invention overcomes these problems by incorporating conductive carbon black into molding compound compositions, such as sheet molding compound compositions, to increase the electrical conductivity of the compositions for use with electrostatic painting.